Hello, I knew JA2 since I was kid, but was too dumb to figure this game out. Through course of years I made several attempts to beat this game, but was failing, but nvm.

I am starting again on latest 1.13 build, and I have a question. I made IMP merc for stealth-assassin playstyle. I can fairly handle eliminating enemies at night. I was wondering if playstyle like this is possible:

My hired mercs engage enemies in firefight, and my IMP stealth merc sneaks up to them from flank or behind and assasinates them. So far I did not do well, they were constantly spotting my AIM. Are this game mechanics capable for playstyle like this one, or is it just me scrubbing?

Stealth is definitely possible but not that easy since you need to see the enemies before they see you, at night you need the best night vision goggles and max possible camoflage according with the terrain you are gonna stealth. Of course if you make mistakes and alarm the enemies, it will be even harder to stealth cause they will run like crazy trying to spot you.

You mean, in close combat, hand to hand or the like? afaik, no.
If you mean sneaking around to engage from different angle (but still at range) it should be possible to an extent, and even useful, but also risky depending where other enemies might be, and decisions the flanked ones take.

Hell, you don't even need a distraction if you have a spy. I always start the game hiring Elroy and getting a disguise and I can reliably take out sectors with 20+ enemies with him alone (with a tiny bit of savescumming ).